Hot standby read slaves exceed max delay on WAL segment. Replication lag.

We've been trying to look into a situation where we're seeing that hot standby read slaves are receiving WAL segments, but are exceeding max_standby_archive_delay (60s) and max_standby_streaming_delay (60s) and not applying changes. The slave will get the first segment and hang (we've seen up to 30m before removing the slave from our read pool to catch up) and get further and further behind the master. Furthermore, we have seen that after a slave has caught up, putting it back into the read pool will mean will almost immediately start to see this happen again. It acts as if we had max_standby_* set to -1.